In order for a train to move along its guideway (i.e., track), it must receive authorization. More particularly, a guideway traffic-control process requires that the train receive authorization to occupy and/or proceed along segments of the guideway, also referred to as blocks, which lie ahead or behind the segment that the train currently occupies.
A train running on a rail network must therefore be able to report its position, or have its block occupancy reported, to a control center. This enables the control center to determine the precise track segment that the train occupies. Among other vital functions, this is information is required so that the control center does not route another train onto the same track segment.
In order to perform vital (i.e., safety-critical) reporting of block occupancy on a railway, track circuits are typically used. And in order to increase the performance of a railway, modern systems comprises location determining systems that use satellite-aided (GPS) positioning techniques, sometimes in conjunction with inertial components (e.g., accelerometers and gyroscopes, etc.) to precisely report train position. In these applications, a “guideway” or “track” database forms a vital component of the guideway traffic-control process.
A guideway database store track information including the absolute and relative position of tracks and track transitions such as, for example, switches and turnouts. Ideally, railroad tracks are perfectly uniform and remain consistent with their original design as straight tangent sections connected by constant curve and spiral sections. In practice, however, weather and geographical conditions, train speeds, tonnage, and continued maintenance requirements contribute to railroad track non-uniformities. Furthermore, track surveys are rarely conducted with the accuracy required for positive train control.
Inaccuracies in a guideway database raise several serious safety concerns. One such concern is the not unusual incidence of a disparity between the output of a train's location determining system and the corresponding database information. Sometimes, reconciling these disparities sufficiently to resolve to a specific track (i.e., locate the train as being on a specific track at a specific position) with a high degree of confidence is problematic.
Also, the Federal Track Safety Standards (FTSS) divide railroad track into nine (9) speed-related classifications as a function of speed, with permissible variations of track geometry provided for each track class. Although the FRA (Federal Rail Administration) regulates the amount of track irregularities permitted for each track class, most track database information carries errors that can change with time and which are often difficult to and expensive to ascertain with accuracy.
The need for an accurate guideway database is clear. But techniques for creating and maintaining an accurate guideway database are quite costly. Typically, the guideway database is generated via separate systems under non-operational conditions. It would, therefore, be beneficial to develop less expensive and more expeditious ways for creating, maintaining and monitoring a guideway database.